Mannosylinositol Phosphorylceramide Biosynthesis Is Required for Cell Surface Adaptation to Ethanol Stress in <i>Saccharomyces cerevisiae</i>

Saccharomyces cerevisiae exhibits a remarkable ability to tolerate high concentrations of ethanol during fermentation, yet the molecular basis underlying this adaptive trait remains incompletely understood. Here, we identify the biosynthesis of the complex sphingolipid mannosylinositol phosphorylceramide (MIPC) as a key determinant of ethanol tolerance in S. cerevisiae. Cells lacking the MIPC synthases Csg1 and Csh1 exhibited pronounced ethanol hypersensitivity and loss of viability. This defect was associated with impaired maintenance of cell wall integrity under ethanol stress and was further exacerbated by disruption of the Rim101 transcription factor or the cell wall integrity MAP kinase Slt2 pathway. Notably, ethanol exposure triggered Rim101-dependent eisosome remodeling specifically in MIPC-deficient cells, indicating altered plasma membrane organization in response to ethanol stress. Hypersensitivity of MIPC-deficient cells extended to alcohols with different carbon chain lengths, suggesting a broader defect in alcohol-induced cellular stress responses. Consistent with these defects, MIPC-deficient cells showed reduced growth and survival under high-glucose fermentative conditions that promote ethanol production. Together, our findings demonstrate that MIPC biosynthesis supports cell surface adaptation to ethanol stress by maintaining cell wall integrity and regulating plasma membrane organization, providing new insights into ethanol tolerance and its relevance to fermentation performance.